var js = 1.0;

 Version = parseInt(navigator.appVersion);

 if (navigator.appName == "Netscape")
     js = ((Version >= 4) ? 1.2 : ( (Version == 3) ? 1.1 : 1.0 ));
 else
     if (navigator.appVersion.indexOf('MSIE') != -1)
         js = ((Version >= 4) ? 1.1 : 1.0);

function changeImages(oldImage) {
   n = Math.random() * 3
   if (n == 1) n = 0
   n = parseInt(n) + 1
   if (js > 1.0) document [oldImage].src = eval('a' + n + ".src");
 }

 if (js > 1.0) {
     a1 = new Image();
     a1.src  = "imgs/imgs_trator1.gif";
     a2 = new Image();
     a2.src  = "imgs/imgs_trator2.gif";
     a3 = new Image();
     a3.src  = "imgs/imgs_trator3.gif";
}